1. Field of the Invention
This invention generally relates to the field of electrical safety compliance testing, and more particularly to a high voltage switching matrix for supplying different test voltages to selected output ports of a multi-function safety compliance test instrument. The selected output ports correspond to different test “channels” and are arranged to scan, or sequentially perform a plurality of safety compliance tests on, multiple devices (“devices under test” or DUTs).
According to the invention, the high voltage switching matrix uses a shared high voltage/continuity input to reduce the number of relays required to switch between the multiple output ports.
2. Description of Related Art
Electrical safety compliance test instruments are used by manufacturers to test electrical products for hazards such as insulation or ground faults that could cause injuries to purchasers and users of the products. Conventional safety compliance tests include continuity, ground bond, AC and DC dielectric withstand or “hipot,” insulation resistance, line leakage, and run tests. For convenience, it is common for safety compliance instruments to be capable of performing more than one of these tests.
Descriptions of various types of safety compliance tests and multi-function safety compliance test equipment may be found in commonly-assigned U.S. Pat. Nos. 6,011,398; 6,054,865; 6,515,484; 6,538,420; and 6,744,259, each of which is incorporated by reference herein. Common safety compliance tests, which may be used both to facilitate product design and during manufacture, include line leakage, insulation resistance, and ground bond tests, as well as various types of dielectric withstand tests. The detailed descriptions in the above-cited patents illustrate the diversity of safety compliance tests that currently must be performed in various situations. For example, line leakage safety compliance testing is primarily used during development of a product to verify whether a design is safe by simulating possible problems which could occur if the product is faulted or misused while the product is operating under high line conditions (110% of the highest input voltage rating of the product), and measuring the amount of current to which a user of an electrical device is exposed. On the other hand, insulation resistance tests are used during design of a product to measure circuit-to-ground impedance by measuring leakage current when a non-destructive voltage (in general, lower than 1000 volts) is applied between the circuit and ground, while dielectric withstand or “hipot” safety compliance tests may be required either during design or manufacturing to measure insulation integrity by subjecting a device to voltages substantially greater than those applied during normal operation (in general, twice the normal operating voltage, plus 1000 volts), and measuring all stray current. Finally, ground bond tests are used during design or manufacturing to measure the response of the ground circuit to potential fault currents that might result from defective insulation, while continuity tests are used to detect short circuits and verify the electrical integrity of a product after assembly.
In order to facilitate testing of large numbers of products, many multifunction safety test instruments are equipped with scanners, which provide test currents and voltages to multiple output ports so that the same tests can sequentially run on more than one product in a single test run. The scanner includes a switching matrix capable of switching between high and low voltages as required for different tests, and for supplying the high and low voltages to each of the output ports. FIG. 1 shows a “scanner matrix board” 69 used in the multifunction tester of U.S. Pat. No. 6,054,865. The scanner provides eight high voltage ports and eight low voltage ports corresponding to output channels CH1 to CH8. Each “channel” is capable of being set to a high or low level. The various connection between the scanner ports or jacks are accomplished by a plurality of relays RY1–RY8 for switching the low voltage input 1300 from an amplifier board between current output jacks 37–44, relays RY19–RY26 for switching the high voltage input from high voltage control board 68 between high voltage scanner high voltage jacks 28–36, and relays RY10–RY17 for selectively connecting output jacks 29–36 to return jack 28 when relay RY18 is closed. In addition, relay RY9 ties the return jack 28 to the ground/common jack 55 when closed.
Not counting relays RY9 and RY18 which switch between different return/ground configurations, this switching arrangement requires 24 relays RY1–RY8, RY10–RY17, and RY19–RY26, one relay at each output jack for connection to the high voltage input 1200, one for the low voltage input 1300, and one for connection to the return 28. All of these relays are required to carry high voltages and/or currents, and therefore are relatively expensive. In general, a conventional switching matrix with m different voltages to be switched between n output ports requires at least m×n relays, and thus the cost increases rapidly for each added voltage or output port.
In addition to the commonly assigned patents cited above, which disclose multi-function test instruments with scanners, or that can be connected to scanners, the following patents may be of background interest: U.S. Pat. Nos. 5,652,526 and 6,538,420 disclose conventional high/low voltage switching arrangements, but the matrices lack multiple channel outputs, while U.S. Pat. No. 6,566,890 discloses a switching matrix for multiple channels that lacks high and low voltage inputs.